This application claims benefit of Japanese Patent Application No. 2000-151537 filed in Japan on May 23, 2000, the contents of which are incorporated by reference.
The present invention relates generally to a zoom lens, and more particularly to a wide-angle, high-magnification zoom lens system well fit for cameras, etc.
High-magnification zoom lenses for cameras have been developed in the fields of studio television cameras and chine cameras for a relatively long time now. With the widespread use of video cameras, zoom lenses for commercial use and domestic use have been under development. For zoom lens systems having high magnifications yet a field angle of 70xc2x0 or greater on the wide-angle side, it is known that a sophisticated level of optical design is needed. One well-established type of zoom lens system is comprised of, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, as typically set forth in JP-B 02-48087. This zoom lens system is characterized in that the first and fourth lens groups remain fixed during zooming.
This type has been extended to a version where a front converter is located in the first lens group, as typically disclosed in U.S. Pat. No. 3,682,534. These zoom lens systems have comprised a number of lenses and so increased in size. The first lens group has mainly been used for focusing.
In recent years, a wide-angle, high-magnification zoom lens system comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, wherein the second, third and fourth lens groups are movable during zooming and focusing is carried out by the fourth lens group, has been proposed, as typically shown in JP-A 06-148520.
Another zoom lens system of the same type comprising, in order from its object side, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, wherein all the lens groups are movable during zooming, has been proposed as typically shown in JP-A 07-20381.
These zoom lens systems have simple lens arrangements, but they would have difficulty in application to future image pickup devices comprising an increasing number of pixels.
Rather, such zoom lens systems have been developed for use on cameras employing conventional silver-salt films. For instance, U.S. Pat. No. 4,299,454 discloses a zoom lens system having a field angle of 80xc2x0 or greater at its wide-angle end and comprising, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power, a third lens group of positive refracting power and a fourth lens group of positive refracting power, wherein the respective lens groups are movable for zooming.
JP-B 58-33531 comes up with a zoom lens system having a zoom ratio of about 5 at a field angle of about 74xc2x0 to about 19xc2x0. Comprising, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power, a third lens group of positive refracting power, a fourth lens group of negative refracting power and a fifth lens group of positive refracting power, this zoom lens system is characterized in that the first and second lens groups are integrated together for focusing.
U.S. Pat. No. 4,896,950 proposes a zoom lens system including a field angle of about 74xc2x0 to about 8.3xc2x0. This zoom lens system comprises, in order from its object side, a first lens group of positive refracting power, a second lens group of negative refracting power, a third lens group of positive refracting power, a fourth lens group of negative refracting power and a fifth lens group of positive refracting power, with the first lens group remaining fixed during zooming.
These zoom lens systems offer no problem when used in silver-salt film camera applications; however, they cannot be used as such for the purpose of taking advantage of aperture efficiency including microlenses used with CCDs for future digital cameras. In consideration of color variation problems inclusive of chromatic aberrations, optical designs are still increasingly required, in which the angle of emergent chief off-axis rays is taken into full consideration possibly with field illuminance in mind.
The primary object of the present invention is to develop a wide-angle, high-magnification zoom lens system best suited for use on cameras, etc.
Some conventional video cameras have been proposed as wide-angle, high-magnification zoom lens systems. However, never until now is any optical system of optical performance well compatible with high-pixel image pickup devices proposed. Silver-salt camera-oriented optical systems leave much to be desired in conjunction with their optical performance and their compatibility with CDs.
In consideration of an image pickup device comprising a microlens, the influences of aliasing due to chromatic aberrations, etc., there is thus a growing demand for an optical system that is a sort of conventional video camera-oriented zoom lens system with some telecentric performance added thereto.
Used primarily with an imaging device having a relatively large image circle, the zoom lens system of the present invention increases extraordinarily in size when optically designed on the basis of a conventional video camera-oriented zoom lens system, often presenting a practically grave problem.
In view of such prior art states as mentioned above, an object of the present invention is to provide a compact zoom lens system which is applicable to a relatively large image-formation device, can maintain sufficient image-formation capabilities at a wide-angle end of greater than 70xc2x0 and at a zoom ratio of greater than about 10, and has a proper focusing mode.
According to the present invention, this object is attainable by the provision of a zoom lens system comprising in order from an object side thereof, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, wherein:
for zooming from a wide angle end to a telephoto end of said zoom lens system, said first lens group to said fifth lens group are all movable,
during said zooming, said first lens group and said third lens group move toward said object side in such a way that a spacing between said first lens group and said second lens group becomes wide and a spacing between said third lens group and said fourth lens group becomes wide,
at least said fourth lens group or said fifth lens group makes a non-linear movement, thereby compensating for a fluctuation of an image plane position with zooming, and
focusing to an finite object is carried out by moving said first lens group and second lens group as an integral unit.
The present invention also provides a zoom lens system comprising in order from an object side thereof, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, wherein:
for zooming from a wide angle end to a telephoto end of said zoom lens system, said first lens group to said fifth lens group are all movable,
during said zooming, said first lens group and said third lens group move toward said object side in such a way that a spacing between said first lens group and said second lens group becomes wide and a spacing between said third lens group and said fourth lens group becomes wide,
at least said fourth lens group or said fifth lens group makes a non-linear movement, thereby compensating for a fluctuation of an image plane position with zooming, and
focusing to an finite object is carried out by moving second lens group.
Further, the present invention provides a zoom lens system comprising in order from an object side thereof, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having negative refracting power and a fifth lens group having positive refracting power, wherein:
for zooming from a wide angle end to a telephoto end of said zoom lens system, said first lens group to said fifth lens group are all movable,
during said zooming, said first lens group and said third lens group move toward said object side in such a way that a spacing between said first lens group and said second lens group becomes wide and a spacing between said third lens group and said fourth lens group becomes wide,
at least said fourth lens group or said fifth lens group makes a non-linear movement, thereby compensating for a fluctuation of an image plane position with zooming, and
focusing to an finite object is carried out by moving together said fourth lens group and said fifth lens group.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.